This invention relates generally to injection molding apparatus having a valve pin member extending in a valve sleeve member, and more particularly to improved apparatus for reciprocating them axially to control the flow of two different fluids through a gate into a cavity.
It is well known in the art to coinject two different plastic melts at the same time and it is also known to sequentially inject them one after the other. U.S. Pat. No. 4,917,594 to Gellert et al which issued Apr. 17, 1990 shows valve gated apparatus for injecting melt through the gate around a central stream of air.
In the past, control of the flow of two or more fluids through the gate into the cavity has been provided by rotating a valve pin member to align different fluid channels and/or by axially reciprocating a valve pin member and one or more valve sleeve members between retracted open and forward closed positions. In U.S. Pat. No. 4,789,318 to Ehritt which issued Dec. 6, 1988, the valve pin member is rotated between different positions to provide coinjection and sequential injection molding. U.S. Pat. No. 4,657,496 to Ozeki et al which issued Apr. 14, 1987 shows reciprocating a valve pin member and valve sleeve member axially to provide sequential injection of two different melts. Netherlands patent application Ser. No. 8900655 to Stork Plastics Machinery B.V. published Apr. 2, 1990 discloses actuating a hollow valve pin member and a valve sleeve member axially to coinject two separate melts around a central stream of air. U.S. Pat. No. 3,947,177 to Eckardt which issued Mar. 30, 1976 describes axially actuating two valve sleeve members and a valve pin member to control coinjection of three separate melts. In these previous arrangements, the valve pin member and valve sleeve member are actuated directly by pneumatic or hydraulic pistons. This has the disadvantages that there is no provision for fine adjustment of the gate opening and closing or accurate control of its timing.